Improved burnisher



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PATENT 1i Fries.

IMPROVED BUFlNlSHER.

Specification forming part of Letters Patent No. l9,{b, dated April 20,1858.

To all whom it may concern:

Be it known that I, CHARLES FRAMPTON, of the city of Brooklyn and Stateof New York, have invented new and useful Improvements in Tools, knownas Burnishers, to be used in Spinning Metals, of which the following isa full and clear description and representation, reference being had tothe drawings herewith filed, making part of this specification, inwhich- Figure 1 is a perspective View, and Fig. 2 a crosssection, of myburnisher.

That part of the burnisher which, in use, is held in the hand I makenearly square in section, the better to hold it in any requiredposition. At the end which is applied to the work, which I make aboutthree-fourths of an inch wide and about one-fourth of an inch thick, Iround off one of the long edges in such a manner that the roundingextends to the opposite edge, leaving said opposite edge sharpthat is,the rounded part extends about a quadrant. From this quadrant toward thehandle I make the surface of the burnisher nearly fiat for the distanceof about an inch. Commencing at the sharp edge, at the end of theburnisher, and continuing the same up over the rounded and flat partsthereof toward the handle, I out two or more grooves rounded in crosssection at the bottom, leaving three or more ribs at their sides roundedin cross-section on their tops. These grooves and ribs should -be ofuniform depth and height throughout, except at their termination towardthe handle. The grooves should slope up easily into the flat surface.The grooves should be a little wider than the ribs. The perspective viewof my burnisher and the cross-section shown in the drawings clearlyillustrate the peculiarities I have described.

The art of metal spinning as formerly practiced required only aburnisher with a single rounded end; but when the production ofscrew-threads on sheet-metal cylinders and cones was introduced I foundthe process of producing them by the use of the spinningburnisherformerly in use was exceedingly slow and unsatisfactory. While pressingin the thread at one point there was a tendency to draw it out slightlyin another, thus marring its accuracy. Its hold upon the blank was alsoinsufficient, there being danger that the tool would not follow thethread, but run di rectly around, causing the threads on the chuck orformer to cut through, the sheet metal, and when the tool did follow thethread or spiral groove between the threads the tend ency of the tool todraw the metal up out of the grooves on each side of the one in which itwas operating rendered it necessary to go over the work so many times,pressing always on the bottom of the groove, that it had a tendency towear out the metal in the groove, making the screw imperfect in fit,destroying its air tight qualities, and often cutting it through, andall these evils were aggravated by the fact that the whole pressure ofthe tool came upon a single point. These are some of the evils whichprompted me to the invention of my improved grooved burnisher forspinning screws.

In my improved burnisher the grooves have at all points the depth of thethreads to be spun, so that the pressure of the tool in finishing thescrew is divided among the bottoms of several grooves and the tops of-several threads, which overcomes the tendency to wear out and cutthrough. The several ribs also overcome the tendency to draw up, abovementioned, as each part is pressed in at the same time, thus completingthe screw and giving it a perfect form in a small fraction of the timerequisite with the old tool, for to Whatever extent the sheet metal ispressed in it will remain, and thus, when once carried as "deep asrequired, it will not need to be run over and over again, as with theold tool, to counteract the drawing up, and the injury to the metal isavoided. The several ribs also take a firmer hold between the threads,and thus overcome the tendency to miss the groove and run directlyaround with the consequences above mentioned. It will thus be readilyperceived that my grooved or many-pointed burnisher is not a meremultiplication like a many-pointed chaser,which merely cuts the more'asit has the more points; but that it operates in a manner radicallydifferent in character from the old burnisher, and that the bottom ofthe grooves performs an important function wholly distinct from meremultiplication of points, so that if the bottoms of the

